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The launchers consisted of a steel tube closed at one end by a steel baseplate, resting on a wooden platform. The 675-pound (306 kg), 5-foot-long (1.5 m), 13-inch-wide (330 mm) shells fit around and on top of the tube, instead of being dropped inside, comprising a type of spigot mortar. The range of each shot was adjusted by adding different size powder charges at the base of the round. The barrels could only handle five or six shots apiece before becoming damaged and unusable. When used in large groups, as was often done, it produced a fearsome effect known as "the screaming Jesus" to U.S. Marines.[1] To absorb the massive recoil caused by firing their projectiles, the mortar tubes were almost always placed up against a mound of dirt.[2]

Japanese officers believed the 320 mm spigot mortar's most effective method of employment was as a psychological weapon, intended to scare American soldiers more than inflict casualties.[5] The 675-pound (306 kg) shells left craters 8 feet (2.4 m) deep and 15 feet (4.6 m) wide, but caused relatively few casualties due to minimal fragmentation.[5] The mortars were mainly operated by the 20th Independent Mortar Battalion.[1]

During the Iwo Jima campaign, many of the 12 to 24 launchers were placed inside the mouths of caves to protect them from American artillery bombardment, requiring the gun crews to live in the caves that housed their guns, like the infantry.[5] Due to the relative difficulty[2] involved in moving such a massive weapon system, their locations usually remained fixed during battles. During the campaign, the object of the gun crews seemed to be mainly to inflict psychological damage on the American troops instead of killing them.[6]